In Vitro Aligners Force Analysis in the Maxillary Arch During En-Masse Retraction With Different Attachment Positions

This study aimed to analyse the three-dimensional forces acting on maxillary teeth with aligners activation of en-masse retraction based on the different attachment positions in vitro.

Three groups were designed for the same 0.25 mm en-masse retraction forces with three different attachment positions. Group A1, without attachments; Group A2, with buccal attachments on maxillary posterior teeth; and Group A3, with lingual attachments on maxillary posterior teeth. Each group consisted of 12 aligners. Aligner forces were measured on a six-axis force transducer measurement system in real time.

In Group A1 and A2, lingual and extrusive forces were observed on incisors, and canines primarily received distal forces. Mesial and lingual forces were both seen on posterior teeth. The forces on anterior teeth in Group A2 were significantly greater, and those on posterior teeth were significantly smaller than Group A1 (p < 0.05). In Group A3, lingual and extrusive forces on incisors and distal forces on canines were significantly greater than those in Group A1 and A2 (p < 0.05), while posterior teeth showed significantly smaller mesial and lingual forces (p < 0.05).

The position of attachments on maxillary posterior teeth significantly influences the force distribution on the maxillary dentition. Lingual attachments are more conducive to anterior teeth retraction and posterior teeth anchorage preservation.